|
A Lowitz arc is an optical phenomenon that occurs in the atmosphere; specifically, it is a rare type of ice crystal halo that forms a luminous arc which extends inwards from a sun dog (parhelion) and may continue above or below the sun.〔Definitions of Lowitz arcs: * (Dictionary.com : Arc of Lowitz ) * (Merriam-Webster : Arc of Lowitz )〕〔(Atmospheric Optics: Computer generated images of Lowitz arcs )〕 == History == The phenomenon is named after Johann Tobias Lowitz (or Lovits) (1757 - 1804), a German-born Russian apothecary and experimental chemist.〔For brief biographies of Johann Tobias Lowitz (1757 - 1804), see: * (Encyclopedia.com : Lovits (Lowitz), Johann Tobias ) * German Wikipedia's article: Johann Tobias Lowitz〕 On the morning of June 18, 1790 in St. Petersburg, Russia, Lowitz witnessed a spectacular display of solar halos. Among his observations, he noted arcs descending from the sun dogs and extending below the sun: Original : ''6. Ces deux derniers parhélies qui se trouvoient à quelque distance des intersections du grand cercle horizontal par les deux couronnes qui entourent le soleil, renvoyoient d'abord des deux cotés de parties d'arc très courtes colorées ''xi'' & ''yk'' dont la direction s'inclinoit au dessous du soleil jusqu'aux deux demi-arcs de cercle intérieurs ''die'' & ''dke''. En second lieu ils étoient pourvues des queues longues, claires & blanches ''x ζ'' & ''y η'' , opposées au soleil & renfermées dans la circonference du grand cercle ''afbg''.''〔See: ''Translation'' : 6. These last two parhelia which were at some distance from the intersections of the great horizontal circle by the two coronas which surrounded the sun, sent, in the first place, from the two sides very short colored arcs ''xi'' & ''yk'' whose direction inclined below the sun as far as the two interior semicircular arcs ''die'' & ''dke''. In the second place, they had long tails, bright and white ''x ζ'' & ''y η'' , directed away from the sun and included in the circumference of the great circle ''afhg''. Lowitz formally reported the phenomenon to the St. Petersburg Academy of Sciences on October 18, 1790, including a detailed illustration of what he had witnessed.〔(Atmospheric Optics : Lowitz's sketch of the solar halos and arcs of June 18, 1790 )〕 The illustration included what are now called “lower Lowitz arcs”. However, some scientists (not unreasonably) doubted the existence of the phenomenon:〔See, for example: Hastings, C.S. (1920) ("A general theory of halos," ) ''Monthly Weather Review'', 48(6): 322–330; from page 328: "The arcs of Lowitz are of special theoretical interest on account of their extreme rarity with questionable authenticity … " As late as 1994, Walter Tape stated: "And in spite of subsequent reports of Lowitz arcs (Ling, 1922 ), there seem to be no photographs of them." (Walter Tape, ed., ''Atmospheric Halos'', Antarctic Research Series, vol. 64 (Washington, D. C.: American Geophysical Union, 1994), page 98.)〕 the phenomenon rarely occurs; and since Lowitz arcs were little known, people who witnessed them didn’t always recognize them; furthermore, until the advent of small, inexpensive digital cameras, witnesses rarely had, at hand, cameras to record them, and even if they did have cameras, the cameras weren’t always sensitive enough to record the faint Lowitz arcs. Only since circa 1990 have photographs of what are clearly Lowitz arcs become available for study and analysis.〔See page 252 of: M. Riikonen, L. Cowley, M. Schroeder, M. Pekkola, T. Öhman, and C. Hinz (September 2007) ("Lowitz arcs," ) ''Weather'', 62 (9): 252-256.〕〔Photographs of Lowitz arcs are available at: * (Atmospheric Optics : Lowitz arcs -- Gallery ) * (Halo Reports. blog spot. com : 46° contact arcs ) * (Atmospheric Optics : Reflected Lowitz arcs )〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Lowitz arc」の詳細全文を読む スポンサード リンク
|